Hearing system with enhanced noise cancelling and method for operating a hearing system

ABSTRACT

The hearing system ( 1 ) comprises a filtering unit ( 6 ) for improving a signal-to-noise ratio of an S+N-audio signal (S+N) composed of a desired audio signal (S) and a unwanted audio signal (N), which filtering unit ( 6 ) comprises
         an adaptive filter;   an S+N-input for receiving said S+N-audio signal (S+N);   an N*-input for receiving an N*-audio signal (N*), which is used as an estimate for said unwanted audio signal (N); and   an S*-output for outputting an S*-audio signal (S*) obtained in dependence of said S+N-audio signal (S+N) and said N*-audio signal (N*), which is an approximation towards said desired signal (S);       

     wherein the hearing system ( 1 ) comprises a selecting unit ( 2 ) operationally connected to said filtering unit ( 6 ) for selecting a first input audio signal (In 1;  In 2; . . .  ) from at least two input audio signals (In 1,  In 2 ) and feeding said first input audio signal (In 1;  In 2 ) either to said S+N-input or to said N*-input. Preferably, said selecting unit ( 2 ) is adapted to selecting also a second input audio signal (In 2 ) from said at least two input audio signals (In 1,  In 2 ), which is different from said first input audio signal (In 1 ), and said first input audio signal (In 1 ) is fed to said S+N-input, and said second input audio signal (In 2 ) is fed to said N*-input.

TECHNICAL FIELD

The invention relates to a hearing system, to an adaptive noisecanceller and to a method for operating a hearing system.

A hearing system comprises at least one hearing device.

Typically, a hearing system comprises, in addition, at least oneadditional device, which is operationally connected to said hearingdevice, e.g., another hearing device, a remote control or a remotemicrophone.

Under a hearing device, a device is understood, which is worn in oradjacent to an individual's ear with the object to improve theindividual's acoustical perception. Such improvement may also be barringacoustic signals from being perceived in the sense of hearing protectionfor the individual. If the hearing device is tailored so as to improvethe perception of a hearing impaired individual towards hearingperception of a “standard” individual, then we speak of a hearing-aiddevice. With respect to the application area, a hearing device may beapplied behind the ear, in the ear, completely in the ear canal or maybe implanted.

BACKGROUND OF THE INVENTION

In the field of hearing devices, and in particular of hearing-aiddevices, noise cancelling is an important issue, because backgroundnoise greatly damages speech intelligibility for a user of a hearingdevice.

One known way of cancelling noise in a signal composed of a desiredsignal plus an unwanted signal (noise signal), which interferes withsaid desired signal, makes use of an adaptive filter, which is a filterthat keeps adjusting itself. A corresponding a noise canceller isreferred to as adaptive noise canceller.

From “Noise reduction in hearing aids: An overview”, Harry Levitt,Journal of Rehabilitation Research and Development, Vol. 38 No. 1,January/February 2001, p. 111-121, an adaptive noise canceller is known,which receives at one input a signal from a speech-and-noise microphoneand at another input a signal from a noise microphone. The signal fromsaid noise microphone is fed to an adaptive filter and subtracted fromthe signal from said speech-and-noise microphone. Thereupon, theadaptive noise canceller can output a signal, which is close to thedesired speech signal (speech, with noise subtracted, at leastapproximately).

Many adaptive filters are known in the art and used for noisecancelling. The LMS (least means square) adaptive filtering algorithm,for example, has been developed more than 45 years ago by Widrow andHoff.

It is desirable to provide for an improved noise cancellation.

SUMMARY OF THE INVENTION

Therefore, one object of the invention is provide for an improved noisecancellation. A hearing system, a noise canceller, and a method foroperating a hearing system shall be provided, which provide for animproved noise cancellation.

Further objects emerge from the description and embodiments below.

At least one of these objects is at least partially achieved byapparatuses and methods according to the patent claims.

The method for operating a hearing system comprising a filtering unitfor improving a signal-to-noise ratio of an S+N-audio signal composed ofa desired audio signal and an unwanted audio signal, which filteringunit comprises an adaptive filter, comprises the steps of

-   -   feeding said S+N-audio signal to an S+N-input of said filtering        unit;    -   feeding an N*-audio signal to an N*-input of said filtering        unit, which N*-audio signal is used as an estimate for said        unwanted audio signal;    -   using said filtering unit for obtaining an S*-audio signal in        dependence of said S+N-audio signal and said N*-audio signal,        which S*-audio signal is an approximation towards said desired        signal;    -   outputting said S*-audio signal from an S*-output of said        filtering unit;    -   selecting a first input audio signal from at least two input        audio signals; and    -   using said first input audio signal as said S+N-audio signal or        as said N*-audio signal.

Through this, an improved noise cancellation can be achievable. Theinvention provides for a new degree of freedom in noise cancellation,because at least one input of the filtering unit is not fixedlyconnected to the source of an input audio signal, but the input audiosignal to be fed to said at least one input can be selected out of atleast two input audio signals.

The invention can be particularly advantageous when the location ofsound sources (of desired or unwanted sound) is not fix, but changes,e.g., when a sound source moves, or when a source of desired soundbecomes a source of unwanted sound (noise) and/or a source of noisebecomes a source of desired sound, as it may happen in a discussioninvolving several people.

An audio signal is an electrical signal, of analogue and/or digitaltype, which represents an acoustic signal.

Today's hearing systems frequently comprise more than two inputtransducer units, wherein an input transducer unit is defined tocomprise at least one input converter, in particular at least oneacoustic-to-electric converter. In the case of a hearing system withmore than two input transducer units, the invention enables to choose,which one of the more than two input transducer units shall provide forthe input audio signal used as S+N-audio signal or as N*-audio signal.

It would, e.g., be possible to fixedly assign one input transducer unitto the S+N-input, e.g., a microphone worn by a speaker, and to choosefrom a number of differently positioned further input transducer unitsthat one further input transducer unit, which represents best the noisein the S+N-audio signal, so that an optimized S*-audio signal can bederived by means of the filtering unit.

Vice versa, it would, e.g., be possible to fixedly assign one inputtransducer unit to the N*-input, e.g., a microphone positioned on atable around which several speakers are seated, and to choose from anumber of further input transducer units, each worn by a differentspeaker, that one further input transducer unit, which is worn by thecurrently speaking speaker. Also this way, an optimized S*-audio signalcan be derived.

Said selecting unit allows for different ways of routing input audiosignals to the inputs of the filtering unit. Therefore, said selectingunit can also be referred to as a signal routing unit.

The adaptive filter may implement any possible adaptive filteringalgorithm, e.g., the LMS algorithm of Widroff and Hoff or others. Manyadaptive filters use a certain number of narrow-band bandfilters, singlebands of which are selectively emphasized or suppressed in dependence ofthe input audio signals.

Considered under a slightly different point of view, which emphasizesthe correlation between the audio signals and the corresponding acousticsignals (also referred to as acoustic waves, sound waves or sound), ahearing system according to the invention can be characterized ascomprising a filtering unit for improving a signal-to-noise ratio of anS+N-audio signal representative of an acoustic signal composed of adesired acoustic signal interfered by an unwanted acoustic signal, whichfiltering unit comprises

-   -   an adaptive filter;    -   an S+N-input for receiving said S+N-audio signal;    -   an N*-input for receiving an N*-audio signal representative of        an acoustic signal approximately corresponding to said unwanted        acoustic signal; and    -   an S*-output for outputting an S*-audio signal obtained in        dependence of said S+N-audio signal (S+N) and said N*-audio        signal (N*), which is representative of an approximation towards        said desired acoustic signal;

wherein the hearing system comprises a selecting unit operationallyconnected to said filtering unit for selecting a first input audiosignal from at least two input audio signals and feeding said firstinput audio signal either to said S+N-input or to said N*-input.

In a very advantageous embodiment of the invention, the method comprisesthe steps of

-   -   selecting a second input audio signal from said at least two        input audio signals, which is different from said first input        audio signal; and    -   using said first input audio signal as said S+N-audio signal;        and    -   using said second input audio signal as said N*-audio signal.

In this embodiment, both, the input audio signal fed to the S+N-input,and the input audio signal fed to the N*-input, are selected from the atleast two input audio signals. E.g., if exactly two input audio signalsare available, it is possible to choose their assignment to theS+N-input and N*-input, respectively.

E.g., in a binaural hearing system comprising two hearing devices, eachcomprising one input transducer unit, one worn at the user's left ear,the other worn at the user's right ear, it can be advantageous to(re-)assign the audio signal generated by the hearing devices to theS+N- and N*-input, respectively, depending on which side of the user aspeaker is located.

In one embodiment, the hearing system comprises at least one inputtransducer unit, which is a remote input transducer unit. A remote inputtransducer unit is an input transducer unit, which can be positionedremote from the hearing system user's head during normal operation ofthe hearing system, e.g., a hand-held microphone. This allows to have alarge distance between at least two input transducer units, whichresults in largely uncorrelated input audio signals and, accordingly, inan enhanced noise cancellation.

In one embodiment, at least one of said at least two input transducerunits is an input transducer unit of a mobile communication device.E.g., the microphone or microphones of a mobile phone and/or Bluetoothheadsets for hands-free communication can be used for generating inputaudio signals.

Mobile communication devices, like, e.g., mobile phones or personaldigital assistants, are today widely used and most of them comprise amicrophone and a standardized wireless short-range communicationinterface like, e.g., Bluetooth or USB. When a hearing systemcomprises—at least in one device of the hearing system—a compatibleinterface, it is possible to integrate such a mobile communicationdevice in the hearing system and thus take advantage of the greatavailability of the mobile communication devices for augmenting thehearing system, at least temporarily.

In one embodiment, the method comprises the step of

-   -   transmitting, at least partially in a wireless fashion, input        audio signals from at least one of said at least two input        transducer units to a device of said hearing system, in which        said selecting of input audio signals takes place.

The wireless transmission may make use of any suitable technology, e.g.,Bluetooth technology or proprietary technologies.

In addition or alternatively, a wirebound connection between devices ofthe hearing system, and in particular between at least one inputtransducer unit and said selecting unit, may be provided for.

In one embodiment, at least one of said at least two input transducerunits comprises at least two acoustic-to-electric convertersand—operationally connected therero—a beam forming unit, and the methodcomprises the step of

-   -   using said beam forming unit for obtaining at least one of said        at least two input audio signals.

Accordingly, a beam-formed input audio signal is provided.

We understand under technical beam forming (in this application alsosimply referred to as beam forming) a tailoring of the amplification ofan audio signal with respect to an acoustic signal as a function ofdirection of arrival of the acoustic signal relative to a predeterminedspatial direction. Customarily, the beam characteristic is representedin form of a polar diagram scaled in dB.

Most generically, technical beam forming is always achieved when theoutput audio signals of two spaced-apart input transducers (alsoreferred to as input acoustic-to-electric converters) are processed toresult in a combined output audio signal.

Beam forming is well known in the art. In conjunction with theinvention, it may be used, e.g., for deriving an S+N-audio signal with aparticularly high content of desired signal.

Usually, each of said at least two input audio signals is obtained fromone of at least two input transducer units of the hearing system,preferably from different input transducer units. It is possible thatone input transducer unit provides for two or more input audio signals,in particular, when the input transducer unit comprises more than oneacoustic-to-electric converter.

In one embodiment, said selecting of input signals is controlled independence of input from the user of the hearing system. This may allowthe user to successively select different assignments of input audiosignals to the S+N- and the N*-inputs and finally select that assignmentwhich results in the most-preferred audible signal. This allows for amanual optimization of noise cancellation.

In one embodiment, the method comprises the steps of

-   -   analyzing at least one of said at least two input audio signals;        and    -   controlling said selecting of input signals in dependence of the        result of said analysis.

This allows for an automatic optimization of noise cancellation. It ispossible to dynamically select an input signal for at least one input ofthe filtering unit.

Various techniques for suitable analyses are known to the person skilledin the art. For example, the analyzing comprises at least one of

-   -   classifying said at least one of said at least two input audio        signals according to a set of classes each of which describes a        predetermined acoustic environment; and    -   estimating a signal-to-noise-ratio of said at least two input        audio signals;    -   evaluating speech intelligibility of at least one of said at        least two input audio signals, in particular estimating an        articulation index of at least one of said at least two input        audio signals;    -   determining a direction of arrival of sound of at least one of        said at least two input audio signals.

Classification of current environments according to a set of classeseach of which describes a predetermined acoustic environment is knownfor an automatic selection of hearing programs in digital hearing-aiddevices. In conjunction with the invention, one or preferably all inputaudio signals can be classified in a way known in the art—simultaneouslyor successively—wherein the result of the classification can be used forthe decision of which input audio signal to assign to which input of thefiltering unit.

In one embodiment, said hearing system comprises at least a secondfiltering unit comprising an adaptive filter, and said method comprisesthe steps of

-   -   feeding a third of said at least two input audio signals to an        S+N-input of said second filtering unit;    -   feeding a fourth of said at least two input audio signals, which        is different from said third input audio signal, to an N*-input        of said filtering unit;    -   using said second filtering unit for obtaining an S*-audio        signal in dependence of said third and fourth of said at least        two input audio signals;    -   outputting said S*-audio signal from an S*-output of said second        filtering unit;    -   controlling said selecting of input signals in dependence of the        S*-audio signals output from said S*-outputs of said at least        two filtering units.

In this embodiment, an input audio signal is fed to an S+N- or anN*-input of said second filtering unit, which is different from theinput audio signal fed to the corresponding input of the other filteringunit. It is possible to compare and/or analyze the so-obtained twoS*-audio signals and to thereupon provide the user with the S*-audiosignal which is considered best-suited or with a signal derivedtherefrom. Said third of said at least two input audio signals may beidentical with said first or said second of said at least two inputaudio signals; and said fourth of said at least two input audio signalsmay be identical with said first or said second of said at least twoinput audio signals.

In one embodiment, the method comprises the step of obtaining at leastone, preferably at least two, of said input audio signals by signalsplitting. Details of corresponding embodiments will be given below inthis application.

According to the invention, an adaptive noise canceller for improving asignal-to-noise ratio of an S+N-audio signal composed of a desired audiosignal and a unwanted audio signal, comprises

-   -   at least two signal inputs for receiving one of at least two        input signals each, wherein a first of said at least two input        audio signals is used as said S+N-audio signal, and a second of        said at least two input audio signals is used as an N*-audio        signal, which N*-audio signal is used as an estimate for said        unwanted audio signal;    -   an S*-output for outputting an S*-audio signal, which is an        approximation towards said desired signal, and which is obtained        in dependence of said S+N-audio signal and said N*-audio signal;        and    -   a selecting unit for selecting at least one of said first and        said second input audio signals from said at least two input        audio signals.

In a very advantageous embodiment of the adaptive noise canceller, saidselecting unit is adapted to selecting both, said first and said secondinput audio signals from said at least two input audio signals.

In particular, adaptive noise cancellers for use in a device of ahearing system are envisaged.

The advantages of the hearing systems and the adaptive noise cancellersaccording to the invention correspond to the advantages of correspondingmethods.

Further preferred embodiments and advantages emerge from the dependentclaims and the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention is described in more detail by means of examplesand the included drawings. The figures show schematically:

FIG. 1 a diagram illustrating an adaptive noise canceller according tothe invention;

FIG. 2 a diagram illustrating a hearing device according to theinvention;

FIG. 3 a diagram illustrating a hearing system;

FIG. 4 an illustration of a selecting unit capable of selecting fromfour input audio signals;

FIG. 5 an illustration of an input transducer unit generating threeinput audio signals;

FIG. 6 an illustration of a hearing system according to the invention,with remote microphone and remote control;

FIG. 7 an illustration of an adaptive noise canceller with a controlunit using classifiers;

FIG. 8 an illustration of a detail of a hearing device according to theinvention with a control unit and two filtering units;

FIG. 9 an illustration of a detail of a hearing device according to theinvention with signal splitting.

The reference symbols used in the figures and their meaning aresummarized in the list of reference symbols. The described embodimentsare meant as examples and shall not confine the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates in a schematic diagram of an adaptive noise canceller5 according to the invention. It comprises a selecting unit 2 and,operationally connected thereto, a filtering unit 6. The filtering unit6 comprises an adaptive filter and receives two input audio signals: anS+N-audio signal and an N*-audio signal. The S+N-audio signal, alsoreferred to as primary signal, is composed of a desired signal and anunwanted signal, the latter also referred to as noise or noise signal.The N*-audio signal is an audio signal, which approximately correspondsto said noise signal or resembles said noise signal, and which is usedas an estimate for said noise signal. It is also referred to as noisereference.

By means of the adaptive filter, an S*-audio signal is obtained fromsaid S+N-audio signal and said N*-audio signal. The S*-audio signal isan approximation towards said desired signal.

The selecting unit 2 receives two input audio signals In1, In2 andallows to select, which of the two input audio signals In1, In2 will befed to the filtering unit 6 as S+N-audio signal and which will be fed tothe filtering unit 6 as N*-audio signal. A selecting unit 2 may berealized in any form, e.g., using switches, in particular in digitalform.

It has been found that it can be very valuable to be able to do such aselection, because in certain acoustic situations, it is not obvious,which of two or more input audio signals has to be used as S+N-audiosignal and which has to be used as N*-audio signal when the best noisecancellation shall be achieved.

Since the selecting unit 2 of FIG. 1 receives only two input audiosignals (In1, In2), it allows to choose only between two states: eitherIn1 is used as S+N-audio signal, while In2 is used as N*-audio signal,or In2 is used as S+N-audio signal, while In1 is used as N*-audiosignal.

An adaptive noise canceller according to the invention can be arrangedin any device of a hearing system.

FIG. 2 is a diagrammatical illustration of a hearing device 11 accordingto the invention comprising an adaptive filter 5 as described inconjunction with FIG. 1, wherein the filtering unit 6 is drawn in moredetail. The hearing device 11 furthermore comprises two input transducerunits M1, M2, a signal processor 9 and an output transducer unit 7,e.g., a loudspeaker, also referred to as receiver. M1 can, e.g., be adirectional microphone and M2 can, e.g., be an omnidirectionalmicrophone. By means of M1 and M2, acoustic sound waves (also referredto as acoustic signals) are converted into audio signals In1 and In2,respectively. These are fed to the selecting unit 2, which feeds In1 tothe S+N-input of filtering unit 6 and In2 to the N*-input of filteringunit 6 or vice versa.

The schematic illustration of the filtering unit 6 shows that the noisereference (N*) is fed to the adaptive filter F, the output of which issubtracted from the primary signal (S+N). The resulting S*-audio signalis output from the filtering unit 6 and used as an error-signal for theadaptive filter F. The S*-audio signal, which is expected to have animproved signal-to-noise ratio with respect to In1 and In2, will usuallybe processed further in the signal processor 9 before the result thereofis fed to the output transducer unit 7.

Furthermore, it is possible that the audio signals output from the inputtransducer units M1, M2 are subjected to some signal processing beforebecoming the S+N- and N*-audio signals used in the filtering unit 6 (notshown).

The signal processor 9 is usually adapted to take individual hearingneeds and preferences of the hearing device user into account. This isin particular the case when the hearing device 11 is a hearing-aiddevice.

The output transducer unit 7 may comprise an electrical-to-mechanicalconverter generating acoustic signals (sound waves) or exciting parts ofthe user's hearing, and/or may comprise an electrical-to-electricalconverter for exciting parts of the user's hearing. Whatever signal theoutput transducer unit 7 generates, it will be considered an audiblesignal A, since it is to be perceived by the hearing of the user,regardless of being acoustic signals, mechanical force or electricalvoltage.

FIG. 3 is a diagram illustrating a hearing system 1, comprising twohearing devices 11, 12, a mobile communication device 13 and a remotemicrophone 14. All these devices 11, 12, 13, 14 of the hearing system 1are operationally interconnected, preferably, as indicated in FIG. 3, ina wireless fashion. Each of them comprises an input transducer unit M1,M2, M3, M4, respectively. The input audio signals In1, In2, In3, In4,obtained by means of the respective input transducer unit M1, M2, M3,M4, are transmitted to at least one of the hearing devices 11,12; inFIG. 3 to each of the two hearing devices 11,12.

Each of the two hearing devices 11, 12 generates an audible signal A,A′, and preferably, each of the two hearing devices 11, 12 comprises anadaptive noise canceller according to the invention. A user interface 19may be foreseen at least one of the hearing devices 11, 12, e.g., inform of a knob, which allows the hearing device user to manually selectbetween different routings of input audio signals to an S+N- and anN*-input of a filtering unit. The optimum choice and the optimum noisecancellation will depend on the input transducer units M1, M2, M3, M4and on their position in the sound field composed of desired acousticsignal S₀ and unwanted (noise) acoustic signal N₀.

Both, the mobile communication device 13 and the remote microphone 14have the advantage that they can be positioned at a location remote fromthe user's head, i.e., remote from the hearing devices 11, 12 worn bythe hearing system user. Positioning two input transducer units, fromwhich the S+N- and the N*-inputs of an adaptive noise canceller are fed,in a great distance from each other, is of great advantage for the noisecancelling, because of the low correlation of the so-derived input audiosignals. For example, devices 13 and/or 14 could be positioned far awayfrom devices 11 and 12, either close to a source of desired sound, e.g.,attached to a speaker, or somewhere where noise prevails. In the lattercase, a source of desired sound could be picked up using a closelyfocused beam-formed audio signal in at least one of the hearing devices11, 12.

In case of a binaural hearing system 1 with a left hearing device 11 anda right hearing device 12, the corresponding input transducer units M1,M2 are—under normal operating conditions—positioned not very remote fromeach other. But due to the head shadow effect, it is neverthelesspossible to achieve a good noise cancellation when using audio signalsderived from these input transducer units M1, M2 as input audio signalsIn1, In2 to a selecting unit and filtering unit as described above.

FIG. 4 is an illustration of a selecting unit 2 capable of selectingfrom four input audio signals In1, In2, In3, In4, as it may be used incase of a hearing system 1 like shown in FIG. 3. Any choice of one inputaudio signal to be fed to the S+N-input of the filtering unit 6 andanother input audio signal to be fed to the N*-input of the filteringunit 6 can be made. Of course, similar selecting units for routing ninput audio signals (with n≧2) onto m inputs of a filtering unit withm≧2 inputs are readily constructed.

FIG. 5 is an illustration of an input transducer unit 5 generating threeinput audio signals In1, In2, In3. This is to illustrate that one inputtransducer unit may be capable of providing for not only one, butseveral input audio signals. The input transducer unit M1 of FIG. 5comprises two acoustic-to-electric converters, the output of which isoutput as In1 and In3, respectively. In addition, an input audio signalIn2 is output, which is obtained by means of beam forming unit Bf, e.g.,in a way known in the art, namely by the delay-and-subtract methodwell-known in the field of beam forming.

FIG. 6 is an illustration of a hearing system 1 comprising a hearingdevice 11, a remote microphone constituting a remote input transducerunit 14 and a remote control 15. Most parts of this hearing system 1have already been described in conjunction with FIGS. 2 and 3. But theselecting unit 2 has a control input 21 and is controlled by a controlunit 3. The control unit 3 is operationally connected to said remotecontrol 15, which has a user interface comprising a user control 19 bymeans of which the user can select different routings of input audiosignals In1, In2 to the two inputs of the filtering unit 6.

FIG. 7 is an illustration of an adaptive noise canceller 5 with acontrol unit 3 using classifiers C1, C2, C3. Despite of having to letthe user manually choose different signal routings until a well-suitedhearing sensation is achieved, like in the embodiment of FIG. 6, theembodiment of FIG. 7 allows for a dynamic and automatic optimization ofthe signal routing accomplished by selecting unit 2.

The control unit 3 of the embodiment of FIG. 7 comprises one classifierC1; C2; C3 per input audio signal In1; In2; In3 and a processor 31. Eachof the classifier classifies one input audio signal according to a setof predetermined classes. Classification is well-known in the field ofhearing device, in particular in the field of hearing-aid devices.

In a simple example, each classifier may derive a value indicative ofthe similarity between the current acoustic scene as reflected in therespective input audio signal In1; In2; In3 obtained by the respectiveinput transducer unit and the predetermined acoustic scene described bythe corresponding class, e.g., “pure speech”, “speech in noise”, “noiseonly” and “music” or other classes. From the so-derived values, theprocessor 31 derives, which signal routing in selecting unit 2 is themost promising one for an optimum noise cancelling. If, e.g., inputaudio signal In1 has a value indicating a high similarity to class“speech in noise” and lower values for similarity to the other classes,and input audio signal In2 has a value indicating a high similarity toclass “music” and lower values for similarity to the other classes, andinput audio signal In3 has a value indicating a high similarity to class“pure noise” and lower values for similarity to the other classes,control unit 3 will advise selecting unit 2 to route input audio signalIn1 to the S+N-input of filtering unit 6 and input audio signal In3 tothe N*-input of filtering unit 6. Of course, decision schemes much moreelaborate than sketched in this simple example may be implemented. Andother types of signal analysis than classification may be implemented,e.g., signal-to-noise ratio determination, speech intelligibilityanalysis (e.g. by articulation index), determination of the direction ofarrival of sound using (e.g., using a beamformer), or others.

FIG. 8 is an illustration of a detail of a hearing device with a controlunit 3 and two filtering units 6, 6′. In this embodiment, two S*-audiosignals S*₁,S*₂ are generated, each one by means of one filtering unit(6 or 6′), wherein the inputs of the filtering units 6 and 6′ are fedwith a different combination of input audio signals. Both S*-audiosignals S*₁,S*₂ are used as inputs for the control unit 3, so that anoptimized noise cancellation can be achieved based on the comparison ofsaid S*-audio signals S*₁,S*₂.

It is also possible to steadily automatically vary the signal routing tothe second filtering unit 6′ and store corresponding data, e.g., theso-obtained S*₂-audio signals and/or results of an analysis of these.Based on these data, an optimized routing may be found, which can thenbe used for routing input signals to filtering unit 6. Instead of tryingout different routings in a purely sequential fashion, it is alsopossible to implement several filtering units, which worksimultaneously, and feed them with different combinations of theavailable input signals. From analyzing the corresponding S*-audiosignals, it is possible to steadily check, which routing would providefor an optimum noise cancellation, and adjust the selecting unit 2accordingly, i.e., use the optimized routing for deriving the S*-audiosignal, which is used as basis for the audible signals A to be perceivedby the user.

In one embodiment, at least one, preferably all of the input audiosignals are derived from audio signals, which are obtained by inputtransducer units, by signal splitting and separate noise cancelling inaudio signal components obtained by said signal splitting. A signalsplitting of an audio signal splits up the audio signal into two or moreaudio signal components. For example, an audio signal may be split upinto two or more components, each only containing frequencies in acertain frequency band. Other criteria for dividing an audio signal intocomponents are known to the person skilled in the art and can, ofcourse, be used, too. After a separate noise cancelling in audio signalcomponents fulfilling different criteria, the resulting(component-based) S*-audio signals will typically be combined again forobtaining one final S*-audio signal.

Preferably, the same criterion (or criteria) for splitting is (are) usedfor all audio signals from which input audio signals to be fed to aselecting unit are possibly derived. And all audio signal componentsfulfilling the same criterion (or criteria) are preferably fed to thesame selecting unit, so that these audio signal components can only befed to the same filtering unit.

FIG. 9 is an illustration of a detail of a hearing device according tothe invention with such a signal splitting. Audio signals from inputtransducer units M1 and M2 are fed to a splitting unit 4 and a splittingunit 4′, respectively. In splitting units 4,4′, the audio signals aresplit, e.g., as indicated in FIG. 9, in dependence of frequency, e.g.,by means of a highpass and a lowpass filter. The lowpass filteredcomponents of the audio signals are fed from splitting units 4 and 4′,respectively, to selecting unit 2 as input audio signals In1 and In2,respectively. And the highpass filtered components of the audio signalsare fed from splitting units 4 and 4′, respectively, to selecting unit2′ as input audio signals In1′ and In2′, respectively. In selecting unit2, the assignment of In1 and In2 to S+N-audio signal (S+N)₁ and N*-audiosignal N₁* is made, which are fed to filtering unit 6 for obtainingS*-audio signal S₁*. And in selecting unit 2′, the assignment of In1′and In2′ to S+N-audio signal (S+N)₂ and N*-audio signal N₂* is made,which are fed to filtering unit 6′ for obtaining S*-audio signal S₂*.The S*-audio signal S₁* and S₂* are then combined again for obtainingS*-audio signal S*. This advanced way of adaptive filtering can, ofcourse, well be combined with or applied to embodiments described above,in particular embodiments with control units 3.

It is to be noted, that various units and parts drawn in the Figures aremerely logic units, in particular 2, 3, 4, 4′, 5, 6, 6 , 9, 21, 31, C1,C2,, C3, F, M1, M2, M3, M4. They may be implemented in various ways,e.g., all in one processor chip or distributed over a number ofprocessors; in one or several pieces of software and so on.

LIST OF REFERENCE SYMBOLS

-   1 hearing system-   2 selecting unit-   3 control unit-   4, 4′ splitting unit, signal splitter-   5 adaptive noise canceller-   6, 6′ filtering unit-   7 output transducer unit-   9 signal processing unit, signal processor, digital signal    processor, DSP-   11 hearing device-   12 hearing device-   13 remote microphone-   14 mobile communication device, mobile phone-   15 remote control-   19 user interface, user control, knob-   21 control input-   31 processor-   A, A′ audible signal-   Bf beam forming unit-   C1, C2, C3 signal analyzing units, classifiers-   F adaptive filter-   In1, In2, . . . input audio signals-   M1, M2, . . . input transducer units-   N noise audio signal-   N*, N*₁, N*₂ N*-audio signal-   N₀ noise acoustic signal-   S desired audio signal-   S*, S*₁, S*₂ S*-audio signal-   S₀ desired acoustic signal-   S+N, (S+N)₁, (S+N)₂ S+N-audio signal

1. Hearing system (1) comprising a filtering unit (6) for improving asignal-to-noise ratio of an S+N-audio signal (S+N) composed of a desiredaudio signal (S) and a unwanted audio signal (N), which filtering unit(6) comprises an adaptive filter (F); an S+N-input for receiving saidS+N-audio signal (S+N); an N*-input for receiving an N*-audio signal(N*), which is used as an estimate for said unwanted audio signal (N);and an S*-output for outputting an S*-audio signal (S*) obtained independence of said S+N-audio signal (S+N) and said N*-audio signal (N*),which is an approximation towards said desired signal (S); characterizedin comprising a selecting unit (2) operationally connected to saidfiltering unit (6) for selecting a first input audio signal (In1; In2; .. . ) from at least two input audio signals (In1, In2, . . . ) andfeeding said first input audio signal (In1; In2; . . . ) either to saidS+N-input or to said N*-input.
 2. The system (1) according to claim 1,wherein said selecting unit (2) is adapted to selecting a second inputaudio signal (In2) from said at least two input audio signals (In1, In2,. . . ), which is different from said first input audio signal (In1),and feeding said first input audio signal (In1) to said S+N-input andfeeding said second input audio signal (In2) to said N*-input.
 3. Thesystem (1) according to claim 1, comprising at least two inputtransducer units (M1, M2, . . . ) each comprising at least oneacoustic-to-electric converter, wherein each of said at least two inputaudio signals (In1, In2, . . . ) is obtained from one of said at leasttwo input transducer units (M1, M2, . . . ).
 4. The system (1) accordingto claim 3, wherein at least one (14) of said at least two inputtransducer units (M1, M2, . . . ) is a remote input transducer unit(M4). 5 . The system (1) according to claim 3, wherein at least one (14)of said at least two input transducer units (M1, M2, . . . ) is an inputtransducer unit (M3) of a mobile communication device (13).
 6. Thesystem (1) according to claim 3, wherein an at least partially wirelesstransmission of input audio signals (In1, In2, . . . ) from at least oneof said at least two input transducer units (M1, M2, . . . ) to saidselecting unit (2) is possible.
 7. The system (1) according to claim 3,wherein at least one of said at least two input transducer units (M1,M2, . . . ) comprises at least two acoustic-to-electric converters andoperationally connected therero a beam forming unit (Bf).
 8. The system(1) according to claim 1, which comprises a control unit (3) forcontrolling said selecting of input signals (In1; In2; . . . ) in saidselecting unit (2).
 9. The system (1) according to claim 8, comprising auser interface for receiving input from a user of the hearing system(1), wherein said control unit (3) is operationally connected to saiduser interface and said selecting of input signals (In1; In2; . . . ) insaid selecting unit (2) is controlled in dependence of said input fromsaid user.
 10. The system (1) according to claim 8, wherein said controlunit (3) comprises at least one signal analyzing unit (C1; C2; . . . )for analyzing at least one of said at least two input audio signals(In1, In2, . . . ), wherein said selecting of input signals (In1; In2; .. . ) in said selecting unit (2) is controlled in dependence of theresult of said analysis.
 11. The system (1) according to claim 10,wherein said at least one signal analyzing unit (C1; C2; . . . ) isselected from the group comprising classifier (C1; C2; . . . ); unitcapable of estimating a signal-to-noise-ratio of a signal; a unitcapable of evaluating speech intelligibility, in particular a unitcapable of estimating an articulation index; a unit capable ofdetermining a direction of arrival of sound.
 12. The system (1)according to claim 8, comprising at least a second filtering unit (6′)comprising an adaptive filter (F); an S+N-input for receiving a third ofsaid at least two input audio signals (In1, In2, . . . ); an N*-inputfor receiving a fourth of said at least two input audio signals (In1,In2, . . . ); and an S*-output for outputting an S*-audio signal (S*₂)obtained in dependence of said third and fourth of said at least twoinput audio signals (In1, In2, . ); wherein said S*-audio signals (S*₁,S*₂) output from said S*-outputs of said at least two filtering units(6, 6′) are fed to said control unit (3) and used for controlling saidselecting of input signals (In1; In2; . . . ) in said selecting unit(2).
 13. Adaptive noise canceller (5) for improving a signal-to-noiseratio of an S+N-audio signal (S+N) composed of a desired audio signal(S) and a unwanted audio signal (N), comprising at least two signalinputs for receiving one of at least two input signals (In1, In2, . . .) each, wherein a first (In1; In2; . . . ) of said at least two inputaudio signals (In1, In2 . . . ) is used as said S+N-audio signal(S+N),and a second (In2; In1; . . . ) of said at least two input audiosignals (In1, In2, . . . ) is used as an N*-audio signal (N*), whichN*-audio signal (N*) is used as an estimate for said unwanted audiosignal (N); and an S*-output for outputting an S*-audio signal (S*),which is an approximation towards said desired signal (S), and which isobtained in dependence of said S+N-audio signal (S+N) and said N*-audiosignal (N*); characterized in comprising a selecting unit (2) forselecting at least one of said first (In1; In2; . . . ) and said second(In2; In1; . . . ) input audio signals from said at least two inputaudio signals (In1, In2, . . . ).
 14. The adaptive noise canceller (5)according to claim 13, wherein said selecting unit (2) is adapted toselecting both, said first (In1; In2; . . . ) and said second (In2; In1;. . . ) input audio signals from said at least two input audio signals(In1, In2, . . . ).
 15. Method for operating a hearing system (1)comprising a filtering unit (6) for improving a signal-to-noise ratio ofan S+N-audio signal (S+N) composed of a desired audio signal (S) and aunwanted audio signal (N), which filtering unit (6) comprises anadaptive filter (F), said method comprising the steps of feeding saidS+N-audio signal (S+N) to an S+N-input of said filtering unit (6);feeding an N*-audio signal (N*) to an N*-input of said filtering unit(6), which N*-audio signal (N*) is used as an estimate for said unwantedaudio signal (N); using said filtering unit (6) for obtaining anS*-audio signal (S*) in dependence of said S+N-audio signal (S+N) andsaid N*-audio signal (N*), which S*-audio signal (S*) is anapproximation towards said desired signal (S); outputting said S*-audiosignal (S*) from an S*-output of said filtering unit (6); characterizedby the steps of selecting a first input audio signal (In1; In2; . . . )from at least two input audio signals (In1, In2 . . . ); and using saidfirst input audio signal (In1; In2; . . . ) as said S+N-audio signal(S+N) or as said N*-audio signal (N*).
 16. The method according to claim15, comprising the steps of selecting a second input audio signal (In2)from said at least two input audio signals (In1, In2, . . . ), which isdifferent from said first input audio signal (In1); and using said firstinput audio signal (In1) as said S+N-audio signal (S+N); and using saidsecond input audio signal (In2) as said N*-audio signal (N*).
 17. Themethod according to claim 15, comprising the step of obtaining each ofsaid at least two input audio signals (In1, In2, . . . ) from one of atleast two input transducer units (M1, M2, . . . ) of said hearing system(1).
 18. The method according to claim 17, wherein at least one (14) ofsaid at least two input transducer units (M1, M2, . . . ) is a remoteinput transducer unit (M4).
 19. The method according to claim 17,wherein at least one (14) of said at least two input transducer units(M1, M2, . . . ) is an input transducer unit (M3) of a mobilecommunication device (13).
 20. The method according to claim 17,comprising the step of transmitting, at least partially in a wirelessfashion, input audio signals (In1, In2, . . . ) from at least one ofsaid at least two input transducer units (M1, M2, . . . ) to a device(11; 12) of said hearing system (1), in which said selecting of inputaudio signals (In1, In2 . . . ) takes place.
 21. The method according toclaim 17, wherein at least one of said at least two input transducerunits (M1, M2, . . . ) comprises at least two acoustic-to-electricconverters and operationally connected therero a beam forming unit (Bf),said method comprising the step of using said beam forming unit (Bf) forobtaining at least one of said at least two input audio signals (In1,In2, . . . ).
 22. The method according to one of claim 15, comprisingthe step of controlling said selecting of input signals (In1; In2; . . .) in dependence of input from the user of the hearing system (1). 23.The method according to claim 15, comprising the steps of analyzing atleast one of said at least two input audio signals (In1, In2, . . . );and controlling said selecting of input signals (In1; In2; . . . ) independence of the result of said analysis.
 24. The method according toclaim 23, wherein said analyzing comprises at least one of classifyingsaid at least one of said at least two input audio signals (In1, In2, .. . according to a set of classes each of which describes apredetermined acoustic environment; and estimating asignal-to-noise-ratio of said at least two input audio signals (In1,In2, . . . ); evaluating speech intelligibility of at least one of saidat least two input audio signals (In1, In2, . . . ), in particularestimating an articulation index of at least one of said at least twoinput audio signals (In1, In2, . . . ); determining a direction ofarrival of sound of at least one of said at least two input audiosignals (In1, In2, . . . ).
 25. The method according to claim 15,wherein said hearing system (1) comprises at least a second filteringunit (6′) comprising an adaptive filter, said method comprising thesteps of feeding a third of said at least two input audio signals (In1,In2, . . . ) to an S+N-input of said second filtering unit (6′); feedinga fourth of said at least two input audio signals, which is differentfrom said third input audio signal, (In1, In2, . . . ) to an N*-input ofsaid filtering unit (6); using said second filtering unit (6′) forobtaining an S*-audio signal (S*₂) in dependence of said third andfourth of said at least two input audio signals (In1, In2, . . . );outputting said S*-audio signal (S*₂) from an S*-output of said secondfiltering unit (6′); controlling said selecting of input signals (In1;In2; . . . ) in dependence of the S*-audio signals (S*₂, S*₂) outputfrom said S*-outputs of said at least two filtering units (6,6′). 26.Method for manufacturing an audible signal by means of a hearing system(1) comprising a filtering unit (6) for improving a signal-to-noiseratio of an S+N-audio signal (S+N) composed of a desired audio signal(S) and a unwanted audio signal (N), which filtering unit (6) comprisesan adaptive filter (F), said method comprising the steps of feeding saidS+N-audio signal (S+N) to an S+N-input of said filtering unit (6);feeding an N*-audio signal (N*) to an N*-input of said filtering unit(6), which N*-audio signal (N*) is used as an estimate for said unwantedaudio signal (N); using said filtering unit (6) for obtaining anS*-audio signal (S*) in dependence of said S+N-audio signal (S+N) andsaid N*-audio signal (N*), which S*-audio signal (S*) is anapproximation towards said desired signal (S); outputting said S*-audiosignal (S*) from an S*-output of said filtering unit (6); deriving saidaudible signal from said S*-audio signal (S*); characterized by thesteps of selecting a first input audio signal (In1; In2; . . . ) from atleast two input audio signals (In1, In2 . . . ); and using said firstinput audio signal (In1; In2; . . . ) as said S+N-audio signal (S+N) oras said N*-audio signal (N*).